| Finalizing
our power plant choices raises a number of questions about gearing.
Gearing is depended on tire size. Tire size effects a number of important
parameters including ride height and center of gravity. It would be
extremely useful to be able to model the car, and modify these interrelated
parameters. In the age of computers, this is surprisingly easy and
affordable to do.
For
$70 ($90- a $20 rebate) we purchase a Logitech
Wingman Steering Wheel. Along with the steering wheel comes
a computer racing game called Sports Car GT
(the game can be purchased for $19.95 alone, but what fun
would it be without a steering wheel?).
This
computer racing simulator features GT cars on well known tracks
around the world. The program has been out a while. Skilled game
hackers have dissected the software and created some very useful
additions. These programs allow you to create, modify, and add cars
and tracks to the program. There is also a program that allows you
to tweak the settings to make the game's car behavior physics more
realistic. These additions are available on the Internet for free,
to anyone with the interest and patience to use them.
We
set up the program following step by step instructions available
at Beginner's
Guide to SCGT. Next, we downloaded a couple of copies of Subaru
Impreza's from Discpad's
Garage. Then using a program called V-Edit (see Beginner's Guide
to SCGT for location) and a program called GT Vehicle Editor or
GTVE (see Beginner's Guide to SCGT for location), we modify the
Subaru's parameters, such as torque curve, weight, gearing to match
our plans. Finally, we adjust the game settings to make it even
more realistic using a program called Advanced Options Editor from
The
Norway Pits.
Now,
we are ready to start testing.
The
first question that this simulator might help with is choosing a
final drive ratio. To allow later comparisons to reality, we do
our testing on a local track that our drivers are intimately familiar
with, the Sebring 12 hour course. We create two versions of the
ProEV Electric Imp, exactly the same except for final drive ratio.
We allow them to race controlled by the computer. The winner has
the better ratio. We reset their ratios based on this information
and run again until we narrow it down to the best ratio (3.8).
Now, this ratio is the best for these virtual cars driven by the
computer on the Sebring 12 hour course. It will be different for
different drivers and different tracks, but we have a good starting
point. The stock Impreza (Manual) differential is 3.9.
What testing has really helped us understand is the trade offs
of the different ratios. In a single speed car (we do not use a
gear box), choosing a final drive ratio is a balance of choosing
a gear ratio low enough to get the acceleration out of the slow
corners (~57 Mph) or a ratio long enough to continue to accelerate
to a high top speed (~131Mph).
We make maximum horsepower at 5500 rpm. We need to gear the final
drive to keep the car as close to this point as possible.
Testing
will continue.
Click
the image below to download your own copy of ProEV's virtual Electric
Imp for use with the Sports Car GT racing game. Please note, the
ProEV virtual Electirc Imp file in provided as a .zip file.
You will need to download the Winzip utility program from here
in order to unzip it.
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